Abiotic stressors significantly limit crop production worldwide. Cumulatively, these factors are estimated to be responsible for an average 70% reduction in agricultural production. Plants are sessile and have to adjust to the prevailing environmental conditions of their surroundings. This has led to their development of a great plasticity in gene regulation, morphogenesis, and metabolism. Adaptation and defense strategies involve the activation of genes encoding proteins important in the acclimation or defense towards the different stressors.
The absorption of nitrogen by plants plays an important role in their growth (Gallais et al., J. Exp. Bot. 55(396):295-306 (2004)). Plants synthesize amino acids from inorganic nitrogen in the environment. Consequently, nitrogen fertilization has been a powerful tool for increasing the yield of cultivated plants, such as maize and soybean. Today farmers desire to reduce the use of nitrogen fertilizer, in order to avoid pollution by nitrates and to maintain a sufficient profit margin. If the nitrogen assimilation capacity of a plant can be increased, then increases in plant growth and yield increase are also expected. In summary, plant varieties that have a better nitrogen use efficiency (NUE) are desirable.
Activation tagging can be utilized to identify genes with the ability to affect a trait. This approach has been used in the model plant species Arabidopsis thaliana (Weigel et al., Plant Physiol. 122:1003-1013 (2000)). Insertions of transcriptional enhancer elements can dominantly activate and/or elevate the expression of nearby endogenous genes. This method can be used to identify genes of interest for a particular trait (e.g. nitrogen use efficiency in a plant), genes that when placed in an organism as a transgene can alter that trait.